The embodiments of present invention relates to a field for a liquid crystal display, in particular to a shift register unit and a gate drive device for the liquid crystal display.
A shift register unit in the prior art includes a signal output terminal outputting a gate drive signal. When the gate drive signal is at high level, the shift register unit controls a row of thin film transistors to be turned on; when the gate drive signal is at low level, the shift register unit controls a row of thin film transistors to be turned off.
The liquid crystal display generally utilizes a scan manner of row by row, when scanning a certain row, the corresponding shift register unit outputs a gate drive signal with high level, the remaining shift register units output a gate drive signal with low level, it is obvious that, for a shift register unit, the gate drive signal is at low level for the most time.
During the time that the gate drive signal is at low level, the gate drive signal would be easily suffer the interference of an inputted clock signal and than produce noise. In order to suppress the noise, the shift register unit normally includes a pull-down thin film transistor which is used to pull down the gate drive signal during the gate drive signal is at low level. A node connected to a gate of the pull-down thin film transistor controls the pull-down thin film transistor to be turned on, such that it can pull down the level of the gate drive signal at the signal output terminal.
The existing problems of the shift register unit in the prior art are: usually the node connected to the gate of the pull-down thin film transistor maintains high level at most time, in this way the pull-down thin film transistor maintains turning on at most time, such that it makes a threshold voltage of the pull-down thin film transistor subjected to a large offset. If the threshold voltage of the pull-down thin film transistor keeps increasing, then it would cause the pull-down thin film transistor unable to be turned on, thereby unable to make the contribution of suppressing the noise, and then the performance of the whole shift register unit would be affected.